Hydropower was the earliest means of commercial electricity generation, and currently dominates alternative electricity supply. However, its global capacity for large-scale exploitation is less than six times that currently installed.

Growth of hydropower is slow and its contribution to global electricity supply is falling. Both are due to economic factors, the slow pace of large-scale project construction, the remoteness of high-potential sites, and increasing resistance to the social

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Hydroelectric energy is ultimately solar energy converted through evaporation of water, movement of air masses and precipitation to gravitational potential energy and then to the kinetic energy of water flowing down a slope. That energy was harnessed for centuries through the use of water wheels to drive mills, forges and textile works, before being supplanted by coal-fired steam energy. Electricity generation using water turbines, although first centred on constricted streams, has increasing

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We have seen in this unit that, despite having a high natural abundance, iron is in very short supply because of the insolubility of its oxides and hydroxides. A result of this is that organisms have developed methods for the uptake, transport and storage of iron. Bacteria, in particular, secrete very powerful iron chelators known as siderophores. Of all the iron–siderophore complexes, the iron(III)–enterobactin complex has the exceptionally high stability constant of 1049 mol<

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Nearly all organisms are able to take up iron. However, only a handful of organisms have had their iron-uptake chemistry studied. The organism that has received most attention (other than human) is a single-cell, prokaryotic bacterium (found in the human large intestine and elsewhere), called Escherichia coli (abbreviated to E.coli), a high-resolution image of which is shown in Author(s):

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Once a pregnancy has been established, many couples are anxious to know the sex of their unborn baby. The reasons for this are many, ranging from the prosaic (will the baby be able to use its brother's or sister's old clothes) to the deeply religious (as described for Hindus in Section 2). In many communities there is so much social pressure on mothers to produce the ‘right’ sex (usually male) that infanticide of the ‘wrong’ sex is widely practised. Because this is illegal in most soc

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There is a common belief that life begins at the moment of conception, i.e. when a sperm fuses with an egg. This is a step forward from past years, when life was alleged to start at the time of ‘quickening’, i.e. when a woman could feel her fetus moving inside her. However, both these opinions suffer from an underlying falsehood: that life ‘begins’ at all. Life is a continuum; gametes are produced by living parents, and fuse to produce new living individuals, but unfused gametes are n

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As you can see from the preceeding section, hormones play a crucial role in the maturation of the oocyte. Figure 3 showed you how levels of oestogen and progestogen vary throughout the menstrual cycle, and suggested that hormone balance is important for a woman's fertility, but you can now see how subtle the control really is. Cells have to develop sensitivity to hormones at the times when the hormones are likely to be present, otherwise the entire operation will fail.

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If you look at the chromosomes shown in Figure 8 you will see that they have been lined up in pairs. The members of each pair are of similar shape and size, and unlike the members of other pairs. At a molecular level these distinctions are maintained: the order of the bases in the DNA is very similar in both members of a pair, but is quite different from that found in other pairs. By ‘very similar’ we mean that the order of the particular genes on each chromosome of the pair is the same,

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Now let us go on with our story and assume that we have decided the time is right to have a baby. The primary requirement for conception is that healthy gametes should be produced. We shall therefore look first at how gametes are made, and then examine some of the factors affecting their quality. But we must start with an explanation of what gametes are, and what sets them apart from other kinds of cell. In other words, what makes gametes special? Gametes are the cells that fuse to form a new

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Many people with particular religious beliefs are fundamentally opposed to the use of artificial methods of contraception. In the developing world, where, as you saw above, the population is frequently increasing at an unsustainable rate, this is a particular problem. For Muslims and Roman Catholics (and others), who may nonetheless wish to limit their families, the preferred option is to use natural family planning methods. The most commonplace method, which involves estimating the ‘fertil

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While hormone-containing pills represent a very sophisticated kind of contraceptive, mechanical contraceptives are a straightforward idea: they act by preventing sperm and egg from meeting. Mechanical contraceptives in their simplest form have been around since before Roman times; some are shown in Figure 4. The earliest ‘penis protectors’ were allegedly used less for contraception than as protection against disease, and as a badge of rank.

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The lifetime of reservoirs can vary greatly. Many reservoirs have lasted for over a hundred years, but some may be useful for only a much shorter period—fifty years or so — not because of the general deterioration of the dam as it gets older, but because sediment accumulates in the reservoir. Rivers carry large amounts of mud, silt and sand in suspension, particularly during floods, and when a river enters a reservoir it slows down and the sediment carried in suspension is deposited on th

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By their very nature, reservoirs occupy large areas of land. Lake Nasser, the reservoir created by the Aswan Dam, has an area of 6000 km2, and even in Britain some 250 km2 of land is covered by reservoirs. The largest in the UK is Kielder Water in Northumberland, which covers about 10.5 km2. British reservoirs are generally in upland areas of scenic beauty that are otherwise suitable only for hiking and related pastimes, and as rough grazing for sheep, but res

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Nuclear power generation results from fission of uranium isotopes when bombarded by neutrons. Conventional burner reactors require relatively scarce uranium-235, whereas fast breeder reactors (which have not yet been developed on any significant scale) would exploit more abundant uranium-238.

In the early 21st century over 400 nuclear — mainly burner — reactors produced 16% of global electricity demand.

The UK played a leading role in nuclear power developments during the 1950

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There are several types of diabetes, including two that are common: Type 1 and Type 2. Type 2 is the most common sort of diabetes. Worldwide, about 90 per cent of people with diabetes have Type 2 and about 10 per cent have Type 1. The other sorts of diabetes account for very small numbers of people.

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